This Swedish longitudinal study explored the mental models of matter used by students (aged 16). It reported that students hold several misconceptions about the sizes and behaviour of atoms, particularly in relation to changes of state. The study also identified a range of issues which may be caused by the representation of the structure and arrangement of atoms in textbooks.

Learners’ ideas

• The nucleus does not move.
• The nucleus takes up a significant proportion of the volume within an atom.
• Electrons only move between shells, not within shells.
• The particles represented by circles in figures showing particle arrangements in student textbooks are atoms.
• There was no differentiation between the behaviour of atoms and molecules in phase change.
• Diagrams of particles in a solid may imply that there is no particle movement (such as vibration).
• Student drawings of particle arrangements either under or overestimate particle separations, often learned from the diagrams in student textbooks.
• All liquids and/or all gases are atomic (have atoms of a single type).
• Differences in phases at constant temperature only depend on particle density.
• Increased particle motion can only arise from energy transferred through heating by the sun or a Bunsen burner.
• Atoms become bigger or smaller with the addition or removal of heat.
• The effect of heating is to change the motion of the electrons rather than the atoms.
• A material comprised of different types of atoms cannot be a single substance.

Suggestions

• Ensuring the introduction of the particulate nature of matter to students could contribute to a better knowledge progression.
• Students should be familiar with the basic particle model, including the presence of interactions between particles and the inherent motion of particles, and how these particles are arranged in the different states of matter before they can appreciate how heating increases particle energy and leads to changes of temperature (and pressure in gases) and changes of state.
• Teachers should place emphasis on the connections between the different models presented and the different contexts in which they are used. 

Study Structure

Aims

To investigate the mental models of matter at the particulate level that learners develop.

Evidence collection

Three semi-structured interviews were conducted based on students' atom drawings. The first interview focused on general atom concepts and terminology, probing models of particles, electrostatic interactions, and movement within atoms. In the second and third interviews, students drew a 'general solid,' exploring their understanding of states of matter through questions about differences between phases. Transcripts were analysed using an 'open coding' technique.

Details of the sample

The sample consisted of 18 students, aged 16, equally split across two different schools in different municipalities in the southern part of Sweden. The sample contained both native and non-native Swedish speakers. All students were about to commence an inorganic chemistry course (Chemistry A). Participation was voluntary.